![]() ![]() For example, move to 180° over 2 seconds:īool status = tTargetPos(180, 2)) FORMAT: bool setTargetPos(float newPosition, float timeSeconds) In these cases, the function notifies this by returning “False” rather than “True”, and it reverts to the normal position-only control. Depending on the maximum acceleration and velocity, it may not be possible for the system to reach the target position within the specified time. While the acceleration and deceleration stay the same, the maximum velocity is reduced so that the system takes just the right amount of time to reach the target (it took me a while to figure out the formula for that! If you are interested to see how it works, check out this interactive graph I made). Position and Time – it is also possible to provide a target position and the amount of time the system should take to reach that position. ![]() If you want the acceleration and deceleration to be the same: Trajectory servoTrajectory(20, 15, 12.5) If the default threshold of 0.1 doesn't need to be changed: * Deceleration (units/second^2) - default = same as acceleration * Acceleration (units/second^2) - default = 50 * Maximum Velocity (units/second) - default = 100 * FORMAT: Trajectory(float maxVelocity, float acceleration, float deceleration, float threshold) The “Threshold” is the difference between the current position and target position at which the controller turns off. For servo motors, this would usually be measured in degrees, but the class can actually work in any units (meters, radians, feet etc.). “Units” refers to the unit type used to measure the position of the system. If you are happy with using some of the default values, you can omit parameters from the right side of the instantiation statement… An example of how it works is shown below. In this step, there are several parameters which you can provide, which determine how the controller will function. Next, the class needs to be instantiated. It therefore acts more like a normal DC motor with a speed controller (h-bridge), and shouldn’t actually be called “servo” since it isn’t using any sensor feedback to control its position. However, this also removes the motor’s ability to figure out how far it has turned. In continuous rotation servo motors, the potentiometer is removed so that the output shaft can rotate more than 180°. It is possible to buy “continuous rotation” servo motors, but these aren’t quite the same the name is actually a bit misleading. This limitation is caused by the potentiometer within the servo, which cannot rotate much more than this without breaking. Most servo motors can only turn up to 180°. When you send a new position command to the servo motor (usually in the form of a PWM signal), the controller moves the motor until the error between the target position and the current position is zero. As the output shaft turns, the resistance of the potentiometer changes which allows the controller to determine how far the motor has moved. ![]() Hobby servo motors usually consist of a small DC motor, a gearbox, a controller chip and a potentiometer (rotary variable resistor) connected directly to the output shaft. The image above shows what these types of motor look like a regular servo motor and a micro servo motor are shown. However, in hobby electronics the term “ servo motor” usually refers to a specific type of motor commonly used in small robots and radio-controlled vehicles. This type of system is commonly used in industrial automation, and there are a wide variety of different sensors, motors and control algorithms to choose from. A servo motor is any type of actuator which uses sensor feedback to control the position, velocity or acceleration of the output.
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